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<head><title>SET-LET_star_-ABSTRACTIONP.html -- ACL2 Version 3.1</title></head>
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<h2>SET-LET*-ABSTRACTIONP</h2>to shorten many prettyprinted clauses
<pre>Major Section: <a href="EVENTS.html">EVENTS</a>
</pre><p>
Note: This is an event! It does not print the usual event summary
but nevertheless changes the ACL2 logical <a href="WORLD.html">world</a> and is so
recorded. Moreover, its effect is to set the <code><a href="ACL2-DEFAULTS-TABLE.html">acl2-defaults-table</a></code>, and
hence its effect is <code><a href="LOCAL.html">local</a></code> to the book or <code><a href="ENCAPSULATE.html">encapsulate</a></code> form
containing it; see <a href="ACL2-DEFAULTS-TABLE.html">acl2-defaults-table</a>.<p>
When this flag is set to <code>t</code>, subterms that occur more than once in
a clause are abstracted away with <code><a href="LET_star_.html">let*</a></code>, generally shortening
the displayed size of the clauses. This flag only affects how
clauses are printed. It does not change what terms the theorem
prover manipulates.
<p>
<pre>
:set-let*-abstractionp t ;;; or, (set-let*-abstractionp t)
</pre>
will cause the prettyprinter to do ``let* abstraction'' on clauses
before they are printed. The algorithm finds the maximal
multiply-occuring subterm and extracts it, binding it to some new
variable and replacing its occurrences by that variable. This produces
a <code>let*</code> form. This process is iterated until no subterm occurs more
than once. This process generally takes a little time, but less time
than to print large clauses. The process can greatly reduce the amount of
text produced by the prover.<p>
THIS ONLY AFFECTS HOW THE CLAUSES ARE PRINTED! The unabstracted
clauses are manipulated by the theorem prover.<p>
<pre>
:set-let*-abstractionp nil
</pre>
restores normal clause printing.<p>
The mode is stored in the defaults table, See <a href="ACL2-DEFAULTS-TABLE.html">acl2-defaults-table</a>.
Thus, the mode may be set locally in books.
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